NEW YORK, USA (AFP) — IPhone and iPad maker Apple is already the world’s largest listed company. Now it will be part of America’s oldest and most storied equity index.

The California tech giant will be added to the elite blue-chip Dow Jones Industrial Average on March 19, replacing venerable telecom company AT&T, S&P Dow Jones Indices announced Friday.

With a market capitalisation of US$730 billion, more than US$300 billion above number-two company Google and four times that of AT&T, Apple was a natural fit for the 30-member Dow, S&P Dow Jones Indices said.

They said Apple would ensure adequate representation for the information technology sector on the Dow, which for decades served as a guideline for conservative, value-focused investors and an indicator of the health of US industry.

“As the largest corporation in the world and a leader in technology, Apple is the clear choice for the Dow Jones Industrial Average, the most recognised stock market measure,” said David Blitzer, managing director of the index committee at S&P Dow Jones Indices.

The index dropped AT&T after concluding the Dow was “over-weighted” in telecommunications, Blitzer said. Telecoms will continue to be represented by Verizon.

The addition of Apple marks another key landmark in the evolution of the 119-year-old Dow and the latest confirmation of Apple as an enduring power in the US corporate landscape.

Originally consisting of General Electric and 11 other “smokestack” companies, the Dow index has progressively diversified to include other sectors, such as retail, consumer goods and telecommunications.

Over the years, the comings and goings of the index have marked the shifting fates of companies and the economy.

The first of the modern technology companies to join was International Business Machines, or IBM, in 1932. The index added Microsoft and Intel in 1999 and Oracle in 2009.

AT&T, whose history dates back to the invention of the telephone itself by Alexander Graham Bell, first joined the Dow index in 1939 as American Telephone & Telegraph.

AT&T was run as a monopoly for years before being broken up by Justice Department antitrust regulators in the early 1980s, but has survived on the Dow under various guises through today.

The last round of changes to the blue-chip list in September 2013 saw the departure of aluminum giant Alcoa and the arrival of sports apparel giant Nike.

Apple’s history dates to 1976 when Steve Jobs, a college dropout, working with two friends, launched a personal computing business from Los Altos, California.

The company soared in the 1980s and early 1990s with the Macintosh, which offered consumers pictures and graphics to make word-processing and other key computer functions easy to use.

After a rough patch following Jobs’ departure in 1985, Apple hit its stride again in the late 1990s and has been riding the momentum of a string of hit consumer electronic products like the iPod, the iMac computer and the iPhone ever since.

Jobs died in 2011 and was replaced by Tim Cook as chief executive.

After facing initial scepticism, Cook has won plaudits for successful efforts to build up the iPhone business in China and for marshalling new gadgets that have kept consumers happy and competitors on their toes.

Apple is expected to launch the Apple Watch, a “smartwatch”, on Monday in San Francisco.

The addition of Apple comes only days after the tech-rich Nasdaq Composite Index — in which Apple is a heavyweight — breached 5,000 for the first time in 15 years.

In mid-morning trade on Friday, Apple shares rose 1.4 per cent to US$128.24, while AT&T fell 1.6 per cent to US$33.47.